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为了实现卫星信号的快速捕获,考虑到“北斗二号”B2频段采用的AltBOC(15,10)调制方式由两路QPSK组成,每一路QPSK都包含数据通道和与其正交的导频通道两部分,导频通道没有数据调制,因此可以通过对周期数据进行累加提高信号的信噪比来进行检测.为此采用了基于FFT的“频率补偿和同步块累加”的方法直接确定信号的多普勒频移,同时为了减小搜索空间提出了双数据块的方法,在不改变频率敏感性的前提下,使速度加倍.仿真结果表明,虽然双数据块累加造成了一定的幅值损失,当信噪比为-24 dB时,20ms的数据可以有效完成多普勒频移的估计.
In order to achieve rapid acquisition of satellite signals, taking into account the “Compass ” B2 frequency band AltBOC (15,10) modulation by two QPSK, each channel QPSK contains data channels and its orthogonal pilot channel In both parts, the pilot channel has no data modulation and therefore can be detected by accumulating periodic data to increase the signal-to-noise ratio of the signal. For this purpose, an FFT-based “frequency compensation and sync block accumulation” method is used to directly determine the signal Doppler frequency shift, and in order to reduce the search space proposed a double data block method, without changing the frequency sensitivity under the premise of doubling the speed.The simulation results show that although the double data block accumulation caused by a certain amplitude Loss, when the signal to noise ratio is -24 dB, 20ms data can effectively estimate the Doppler shift.